---
sidebar_position: 2
title: Source
description: "A [subscriber](./index.md) reads a subscription named by a string or by the broker's descriptor, fixed in the attribute or left to the mount site."
---
import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';
# Source
A subscriber reads a subscription named by a string or by the broker's descriptor, fixed in the attribute or left to the mount site.
The attribute fixes the kind of subscription and may leave its value to the mount site:
| `#[subscriber("orders")]` | by name | fixed here |
| `#[subscriber]` | by name | [`.name(..)`](api:ruststream::runtime::SubscriberSettings::name) at the mount site |
| `#[subscriber(MemorySource::new("orders"))]` | the broker's descriptor | fixed here |
| `#[subscriber(MemorySource)]` | the broker's descriptor | `.name(..)` at the mount site |
A name is a [`Name`](api:ruststream::Name) source and works on any broker that implements [`Subscribe`](api:ruststream::Subscribe), which opens its default subscription kind for that name.
A descriptor is a type of the broker crate that implements [`SubscriptionSource`](api:ruststream::SubscriptionSource) and carries the broker's own settings, such as a consumer group or a durable name; the in-memory broker's is [`MemorySource`](api:ruststream::memory::MemorySource).
The macro reads the descriptor's type off the constructor call, so the expression ends in `Type::new(..)` and every step after it returns `Self`.
A descriptor kind that the mount site names implements [`FromName`](api:ruststream::FromName).
A source left open must be named: a mount without `.name(..)` does not compile.
`.name(..)` is one of the mount-site [settings](./mount-settings.md) and takes any string, so the name may come from configuration read before the app is built.
A descriptor kind that needs more than a name, such as a Pulsar topic with its subscription, is written out in full in the attribute.
In the manual form the first argument of `subscriber` is the source: a string, a descriptor, or `Unnamed::<Kind>::new()` for a source the mount site names, an [`Unnamed`](api:ruststream::Unnamed) value.
## Example
The bare attribute leaves the name to the mount site.
<Tabs groupId="api">
<TabItem value="macros" label="Macros">
```rust reference="examples/subscriber_source.rs#name_at_mount"
```
</TabItem>
<TabItem value="manual" label="Manual">
```rust reference="examples/manual/subscriber_source.rs#name_at_mount"
```
</TabItem>
</Tabs>
## The broker's descriptor
A descriptor is fixed in the attribute, or only its kind is, and the name comes at the mount site.
<Tabs groupId="api">
<TabItem value="macros" label="Macros">
```rust reference="examples/subscriber_source.rs#descriptor"
```
</TabItem>
<TabItem value="manual" label="Manual">
```rust reference="examples/manual/subscriber_source.rs#descriptor"
```
</TabItem>
</Tabs>